Beating The Blues With Red-tinted White Lighting
Fierce competition in the backlighting market is squeezing the profits of leading LED chipmakers,which are now trying to boost their margins by targeting general lighting. At Epistar, this had led to the development of highly efficient warm-white sources that combine red and blue chips, explains Epistar’s Shao-You Deng, Special Assistant to the company’s General Manager, in a interview with Richard Stevenson.
RS How do sales of LEDs for general lighting and backlighting compare?
SD In 2011, general lighting contributed roughly 25-30 percent of revenue. We are focusing on increasing this at more than 5 percent per year. LED backlighting for LCD displays is around 50 to 60 percent of revenue. This includes small, medium and large-sized backlights – for example, mobile phones, tablets, TVs and monitors.
RS Are you seeing saturation in the global market for LED display backlighting ?
SD No. The emerging markets are still developing, such as those in India and Africa. Even mainland China does not have that high a penetration rate. Although the quantity of LEDs used in one TV will decrease and the average selling price (ASP) will go down, the total quantity will increase. So it will be a slowly growing market.
RS Is Epistar still able to operate profitably in the display business, given the declines in average selling price?
SD This is hard to say, but we think the answer is yes. Our scale of economy helps us to keep a profit, but it will be a decreasing proportion [of overall profit]. We have not only the display business – we have general lighting, general indicators, and so on.
RS You have a strong history in the manufacture of red and yellow LEDs. Are you the world’s leading manufacturer, in terms of volume?
SD Yes! We estimate that we have more than 50 percent market share. In terms of the performance of these red and yellow LEDs, which we call four-element-material LEDs, we are number one.
Our red and yellow LEDs are used in outdoor and indoor RGB displays, which differ from LCD displays. This is a major application. Other applications are automotive interior and exterior lighting, and indicators for lighting and consumer electronics.
RS You also use red LEDs with blue ones to create white light sources. How easy is it to deliver good colour mixing with that approach?
SD In many LED packaging houses, they can easily put a phosphor on a blue LED. If you put another red chip beside a blue chip and cover them with a phosphor, the phosphor behaves like a diffuser. That means that the colour mixing will be easier than a pure RGB combination, which does not use a phosphor.
RS To make a high-performance white-light source you need good red and blue LEDs. How good are your blue and red LEDs, and what technologies do they employ to deliver those levels of performance?
SD For our red LEDs, the wavelength is around 611 nm. We can deliver about 125 lm/W in mass production with the best bonding and light extraction technologies.
We have different designs. One is the traditional low-voltage LED, and its size is not that large – around 14 mil by 14 mil (350 μm by 350 μm). These can be driven from 20 mA to 40 mA. Our other design is the high-voltage type. This is also 20 mA, but can operate up to 20 V.
Our blue LED can deliver up to 150 lm/W at 5700 K in mass production, by using current spreading and internal quantum efficiency optimization. This LED is also available as a low-voltage and a high-voltage structure.
Testing the reliability of Epistar’s red and yellow LEDs
RS Are there significant advantages in using a red LED, rather than a red phosphor, for making white LEDs?
SD The red LED can significantly boost the CRI (colour rendering index) and the lumen-per-Watt in the region of 2700 K to 3000 K. If you use just a phosphor with a blue chip, efficiency is good at around 5700 K to 4000 K. But below 4000 K, efficiency drops very fast. We have compared these two types of LEDs. Without the red LED, performance drops by 30 percent.
RS Will you take this approach a step further and introduce white-light sources based on red, blue and green LEDs?
SD No. [With our chipsets], the green colour comes from the blue phosphor conversion, rather than a green LED. Green efficiency [with our approach] is now around 90-100 lm/W. The efficiency of a red-green-blue LED would be lower than either a blue LED and just a phosphor, or a blue LED with a phosphor and a red LED. Using a green LED as part of three different chips packaged together also complicates assembly and control.
RS You have developed high-voltage white light sources based on red and blue LEDs. How do these work?
SD The high-voltage LED is a product for the retrofit bulb market. Its voltage is closer to the mains – for example, 120 V, or 110 V. The aim is to bring the LED’s voltage to match the mains, and significantly reduce the driver cost and space, especially for the retrofit bulb application, because there is not enough space to put too much circuitry. The high-voltage LED can be a blue chip with phosphor, or blue and red chips plus a phosphor. But our best high-voltage LED combines blue and red chips, and can be introduced into the warm-white market.
Testing blue LEDs for longterm reliability
RS How do you achieve the high voltage?
SD The voltage for one blue chip is around 3.0 V to 3.3 V. So we put them in series – maybe 10 LEDs, so around 30 V. We are using semiconductor processes to bind them together. Semiconductor technology is well-suited to isolating very small devices and connecting them together.
RS What volumes of these high-voltage white light sources are you shipping today, and how do you project this to increase over the next few years?
SD Now it’s about 3 million per month, and we are focusing on increasing this to 10 million per month by the end of the year.
RS What are the typical performance figures for these white light sources?
SD So far we have three different sets to provide to our customers for these applications. They all have a CCT of 2700 to 3000 K, and a CRI greater than 85.
Our first is the standard set, around 100 lm/W. Our second is the premium set, around 120 lm/W, and the last is the deluxe set around 150 lm/W.
RS What level of efficacy is required to have success in the LED light bulb market?
SD For LED light bulbs, the main markets are for the 40 W, 60 W and 75 W. For the 40 W replacement, we are using the standard set, with 100 lm/W. The 60W replacement uses 120 lm/W, and if you need to go higher to 75 W, you need 150 lm/W. The bulb doesn’t have much space to put the light source and deal with thermal treatment, so efficiency is a big issue.
RS Epistar must have thought about becoming a vertically integrated manufacturer of LED lighting products, such as LED bulbs. Why has the company decided to just be an LED manufacturer?
SD We value our partnership with our downstream customers. We don’t want to be in competition with our clients, and would rather have a win-win situation.
We are focusing on our epitaxial wafer technology, our process technology, and we are trying to help our downstream customers. For example, helping them in how to use LED chips to enhance performance, or how to package them.
RS Has LED lighting made much of an impact in Taiwan?
SD Yes, but it’s not happening fast. The government is placing increasing emphasis on popular LED lighting, and it is changing the streetlights to LED lighting in 2012. A subsidy program for households is also about to launch.
An Epistar technician loading and unloading the LED wafers in a tool for the metallization process
RS You have a joint venture agreement with Toyoda Gosei. Is this a win-win for both companies. Why?
SD Toyoda Gosei has comprehensive worldwide patents, but very limited production capacity in Japan. So it’s invested in a JV (joint venture) company with Epistar. The JV company inherits TG’s patents and is able to use Epistar’s production facility for cost-competitive production. Epistar can penetrate some markets that require special patents.
In the Japanese market, these LEDs are sold under the TG brand. We have another JV office, TE with TG, that’s based in Taiwan and is for sales outside the Japanese market. Therefore, if we want to deliver these chips to other customers, we are able to sell through the TE with TG brand.
RS Do you have any joint ventures with Chinese firms?
SD Yes, we have several JVs with local Chinese firms. This allows us to belong to the downstream of the lighting supply chain. By doing so, we get updates on market demand and the design of lighting products for consumer needs.
RS How do you view the strong package of incentives provided in China for LED manufacture? Has it helped the global LED industry grow revenues by driving down prices, or has it squeezed profits through an oversupply of chips, and ultimately put the brakes on investment?
SD We think that the later claim is a more suitable description for the result of China’s incentives for progress. The oversupply has really been driven by what has happened in mainland China. There is still a shortage of high-end LED chips, which are bright enough to go into the TV market or high-end lighting. But LED makers will struggle if they cannot catch this high-end market.
RS What programmes does Epistar have in place to increase yield and cut the cost per lumen?
SD If you want to get costs down, the best way is to increase your yield. There are two points of view on how to do this: One, to increase your manufacturing efficiency; and two, to increase the efficiency of LED chips.
If you improve the efficiency you improve the lumens. And if you can improve the lumens per area, you can shrink the chip, and that means you can produce more chips with one wafer. So the cost will fall.
RS What do you hope to see from equipment, substrate and materials suppliers in the next year?
SD From equipment makers, we hope to see more customized, consistent equipment to generate more products in the same running time, so our throughput will be higher. For the substrate and materials suppliers, we expect to receive more stable quality, and maybe a more reliable and consistent product.
RS Will Epistar increase its chip capacity this year, and if so, by how much?
SD It’s hard to give you a precise answer. We have some JV in mainland China, so we have different ways to develop capacity. In China, for example, one JV has increased MOCVD capacity, and maybe two or three sites have increased their quality.
RS Do you expect average selling prices of LEDs to tumble, or will reductions in price start to slow over the next few years?
SD For high-end LEDs, the demand is still strong. But overall – because of the environment and the application mix – the price reduction will be fast in 2012. But maybe in 2013 there will be a slowing down in price reduction.
An Epistar technician examines an LED epiwafer
RS How will Epistar’s business evolve, in terms of revenue and profit, over the next two years?
SD The ASP is going down very fast, making it difficult to deliver a large increase in revenue. This year we hope that revenue will grow by 5- to-10 percent – I think that will be hard work to achieve.
With prices dropping very fast, it is hard to maintain profit and revenue at the same time. This year we are focusing on how to improve market share in this downturn, and we are hoping to cover different application fields. Maybe pricing will be stable in 2013, or our technology can improve, so we can make a profit in 2013.
Epistar’s headquarters are located on the Hsinchu Science Park, Taiwan
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Direct-type LED TVs
One promising market for Epistar is direct-type LED TVs.The majority of LED-backlit LCD TVs on sale today have an array of LEDs at the sides of the screen, and use a lightguide to channel the emission from these chips onto the display. One weakness of this approach is the high cost of the lightguide, which can be avoided by using LEDs in a similar way to the more traditional CCFL sources.
In this case, known as direct-type LED TVs, the screen is illuminated by an LED lightbox. This trims the overall cost of the TV, but there is a downside to pay – a thicker screen, which is needed to accommodate the lightbox. Space is needed to mix the emission from a battalion of very high brightness LEDs, and this leads to increases in the distance from the screen, which reduces the need for lightguides and diffusers.